You can decide which features in the WorkingSet of a layer to visualize, by configuring a feature filter on a FeatureLayer. A Feature filter is a function that accepts a LuciadRIA Feature, and returns true if the map must show the Feature. To set the Feature filter, use the filter property on the FeatureLayer:

Program: Setting a filter on a layer. The filter ensures that the map shows only cities with a population smaller than a certain threshold. (from samples/selection/main.js)
citiesLayer.filter = function(feature) {
  return feature.properties.TOT_POP <= value;
};

The configuration of a feature filter doesn’t change the working set of the feature layer. The client still queries all the data from the server, and loads it into memory.

If you want to limit the amount of data that the client queries, you must re-configure the queryProvider on the loadingStrategy of the FeatureLayer. See the Dealing with large feature data sets article for an illustration